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Revision total hip arthroplasty for metal-on-metal failure

Published:October 08, 2019DOI:https://doi.org/10.1016/j.jcot.2019.09.021

      Abstract

      Metal-on-metal (MoM) arthroplasty systems became popular in the early-2000s due to presumed advantages of improved wear characteristics and superior stability. However, subsequent reports of abnormal soft-tissue reactions to MoM implants and national registry data reporting high failure rates raised concerns. Early outcomes of revision total hip arthroplasty (THA) for adverse reaction to metal debris (ARMD) were poor, leading to development of surveillance programs and a trend towards early revision surgery. Patients with MoM arthroplasties require surveillance, comprehensive history and physical examination, imaging with ultrasound or magnetic resonance imaging (MRI), and laboratory evaluation including metal ion levels. Operative strategies for revision THA vary from exchange of modular components to extensive debridement and reconstruction with revision components. Surgeons should be aware of the increased risks of dislocation and infection following revision THA for ARMD. However, there is growing evidence that early revision surgery prior to extensive soft tissue destruction results in improved outcomes and decreased re-operation rates. It is estimated that >1 million MoM articulations have been implanted, with a large proportion still in situ. It is imperative to understand the aetiology, presentation, and management strategies for these patients to optimise their clinical outcomes.

      Keywords

      1. Introduction

      McKee and Watson-Farrar introduced the first metal-on-metal (MoM) total hip arthroplasty (THA)
      • McKee G.K.
      • Watson-Farrar J.
      Replacement of arthritic hips by the McKee-Farrar prosthesis.
      in the 1950’s. However, these initial implants became obsolete as the Charnley technique of low-friction arthroplasty with metal-on-polyethylene bearing surfaces gained popularity in the mid-1970s.
      • Charnley J.
      Total prosthetic replacement of the hip.
      Subsequent generations of MoM implants using cobalt-chromium-molybdenum alloys provided optimism due to theoretical advantages over conventional metal-on-polyethylene bearing surfaces.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      Implantation of thinner metal liners with larger femoral head sizes increased the arc of motion and promised decreased dislocation rates.
      • Pollard T.C.
      • Baker R.P.
      • Eastaugh-Waring S.J.
      • Bannister G.C.
      Treatment of the young active patient with osteoarthritis of the hip. A five- to seven-year comparison of hybrid total hip arthroplasty and metal-on-metal resurfacing.
      In addition, improved wear characteristics and reduced volumetric wear with MoM bearing surfaces provided a potential advantage over metal-on-polyethylene in decreasing the risk of osteolysis associated with polyethylene wear.
      • Fisher J.
      • Jin Z.
      • Tipper J.
      • Stone M.
      • Ingham E.
      Tribology of alternative bearings.
      This led to increased interest and re-introduction of hip resurfacing, which offered an additional benefit of bone preservation on the femoral side.
      • Ball S.T.
      • Le Duff M.J.
      • Amstutz H.C.
      Early results of conversion of a failed femoral component in hip resurfacing arthroplasty.
      These proposed benefits led to increased appeal and widespread uptake of both MoM THA and hip resurfacing. This popularity peaked in the early 2000’s, where 35% of all THA utilised MoM bearing surfaces in the United States.
      • Bozic K.J.
      • Kurtz S.
      • Lau E.
      • et al.
      The epidemiology of bearing surface usage in total hip arthroplasty in the United States.
      However, subsequent reports of abnormal soft-tissue reactions to MoM implants and national registry data revealing unacceptably high revision rates raised concerns.
      • Malviya A.
      • Holland J.P.
      Pseudotumours associated with metal-on-metal hip resurfacing: 10-year Newcastle experience.
      • Kwon Y.M.
      • Ostlere S.J.
      • McLardy-Smith P.
      • Athanasou N.A.
      • Gill H.S.
      • Murray D.W.
      "Asymptomatic" pseudotumors after metal-on-metal hip resurfacing arthroplasty: prevalence and metal ion study.
      • Kwon Y.M.
      • Thomas P.
      • Summer B.
      • et al.
      Lymphocyte proliferation responses in patients with pseudotumors following metal-on-metal hip resurfacing arthroplasty.
      • Anderson H.
      • Toms A.P.
      • Cahir J.G.
      • Goodwin R.W.
      • Wimhurst J.
      • Nolan J.F.
      Grading the severity of soft tissue changes associated with metal-on-metal hip replacements: reliability of an MR grading system.
      • Pandit H.
      • Glyn-Jones S.
      • McLardy-Smith P.
      • et al.
      Pseudotumours associated with metal-on-metal hip resurfacings.
      The Medicines and Healthcare Products Regulatory Agency (MHRA) in the United Kingdom issued an alert in 2010 highlighting reports of reivions of MoM hip arthroplasties involving soft tissue reactions.
      • Medicines and Healthcare Products Regulatory Agency
      Medical Device Alert: all metal-on-metal (MoM) hip replacements.
      Subsequent action included the development of surveillance programs to ensure routine follow-up and investigations with serum ion levels and imaging.
      • Medicines and Healthcare Products Regulatory Agency
      Medical Device Alert: all metal-on-metal (MoM) hip replacements.
      In 2011, The United States Food and Drug Administration (FDA) mandated that manufacturers of MoM THA and hip resurfacing systems perform post-market surveillance and publicly addressed growing concern for abnormal soft tissue reaction and increased revision rate.
      Although MoM THA and hip resurfacing are both associated with ARMD, they have different aetiologies.
      • Haddad F.S.
      • Thakrar R.R.
      • Hart A.J.
      • et al.
      Metal-on-metal bearings: the evidence so far.
      MoM THA is associated with taper corrosion leading to deposition of metal ions in the peri-prosthetic space, often without significant wear of the bearing surfaces. In contrast, ARMD in hip resurfacing is generally secondary to wear of the MOM articulation. It is estimated that the risk of ARMD following hip resurfacing ranges from 0.3% to 3.4% with a maximum mean follow-up of 7.1 years.
      • Malviya A.
      • Holland J.P.
      Pseudotumours associated with metal-on-metal hip resurfacing: 10-year Newcastle experience.
      ,
      • Haddad F.S.
      • Thakrar R.R.
      • Hart A.J.
      • et al.
      Metal-on-metal bearings: the evidence so far.
      ,
      • Langton D.J.
      • Jameson S.S.
      • Joyce T.J.
      • Hallab N.J.
      • Natu S.
      • Nargol A.V.
      Early failure of metal-on-metal bearings in hip resurfacing and large-diameter total hip replacement: a consequence of excess wear.
      Outcomes following hip resurfacing also depend on the implant design, with the Birmingham resurfacing (BHR, Smith & Nephew) outperforming the ASR surface replacement (DePuy). This has led to a recall of specific MoM implant systems including the DePuy ASR XL Acetabular system, Smith & Nephew R3 Acetabular system metal liners, and the Zimmer Durom Acetabular component.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      It has been reported that up to 18% of patients implanted with the DePuy ASR THA system had developed ARMD.
      • Langton D.J.
      • Jameson S.S.
      • Joyce T.J.
      • Hallab N.J.
      • Natu S.
      • Nargol A.V.
      Early failure of metal-on-metal bearings in hip resurfacing and large-diameter total hip replacement: a consequence of excess wear.
      However, these reported figures may grossly underestimate the true prevalence, with one study identifying pseudotumours in 59% of patients with MoM hip prosthesis using metal artifact reduction sequence (MARS) magnetic resonance imaging.
      • Hart A.J.
      • Satchithananda K.
      • Liddle A.D.
      • et al.
      Pseudotumors in association with well-functioning metal-on-metal hip prostheses: a case-control study using three-dimensional computed tomography and magnetic resonance imaging.
      Initial outcomes following revision surgery for MoM implants were poor.
      • Munro J.T.
      • Masri B.A.
      • Duncan C.P.
      • Garbuz D.S.
      High complication rate after revision of large-head metal-on-metal total hip arthroplasty.
      However, these were often performed in the setting of significant soft tissue damage and pseudotumour. It is evident that outcomes following revision surgery is dependent on the indication, with worse outcomes demonstrated with the presence of pseudotumour and abductor deficiency.
      • Haddad F.S.
      • Thakrar R.R.
      • Hart A.J.
      • et al.
      Metal-on-metal bearings: the evidence so far.
      This had led to improved surveillance and adoption of a lower threshold for revision THA.
      • Malviya A.
      • Holland J.P.
      Pseudotumours associated with metal-on-metal hip resurfacing: 10-year Newcastle experience.
      ,
      • Haddad F.S.
      • Thakrar R.R.
      • Hart A.J.
      • et al.
      Metal-on-metal bearings: the evidence so far.
      ,
      • Hart A.J.
      • Satchithananda K.
      • Liddle A.D.
      • et al.
      Pseudotumors in association with well-functioning metal-on-metal hip prostheses: a case-control study using three-dimensional computed tomography and magnetic resonance imaging.
      This has led to a cessation of MoM bearing surfaces for THA and a significant decrease in the number of hip resurfacings performed annually. In 2017, the NJR in the UK reported <0.1% of all hip replacements utilised MoM bearing surfaces. It also reported a decreasing percentage of implanted hip resurfacings (0.6%) compared to all primary hip arthroplasty.
      • National Joint Registry for England W
      Northern Ireland, and the Isle of Man. 15th annual report.
      Despite this, a sizable patient population have MoM implants in situ, and it is estimated that >1 million MoM articulations have been implanted worldwide.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      ,
      • Bozic K.J.
      • Kurtz S.
      • Lau E.
      • et al.
      The epidemiology of bearing surface usage in total hip arthroplasty in the United States.
      It is imperative to understand the aetiology, presentation and management strategies for these patients to optimise their clinical outcomes.

      2. Aetiology

      The deposition of metal ions into the peri-prosthetic space can lead to a wide spectrum of soft tissue reactions including massive sterile effusions, necrosis, corrosive osteolysis, and both cystic and solid peri-prosthetic masses. This spectrum of soft tissue lesions associated with MoM articulations is collectively labelled as adverse reaction to metal debris (ARMD).
      • Pandit H.
      • Glyn-Jones S.
      • McLardy-Smith P.
      • et al.
      Pseudotumours associated with metal-on-metal hip resurfacings.
      ARMD also encompasses the terms metallosis, aseptic lymphocytic vasculitis-associated lesions (ALVAL), and pseudotumour, which have all been used to describe the various presentations.
      • Korovessis P.
      • Petsinis G.
      • Repanti M.
      • Repantis T.
      Metallosis after contemporary metal-on-metal total hip arthroplasty. Five to nine-year follow-up.
      ,
      • Willert H.G.
      • Buchhorn G.H.
      • Fayyazi A.
      • et al.
      Metal-on-metal bearings and hypersensitivity in patients with artificial hip joints. A clinical and histomorphological study.
      Metallosis describes gross macroscopic staining of peri-prosthetic tissues secondary to metal particulate debris.
      • Korovessis P.
      • Petsinis G.
      • Repanti M.
      • Repantis T.
      Metallosis after contemporary metal-on-metal total hip arthroplasty. Five to nine-year follow-up.
      ALVAL is a specific histological diagnosis that exhibits a lymphocyte dominated immunological response and can occur throughout all severity and stages of ARMD.
      • Willert H.G.
      • Buchhorn G.H.
      • Fayyazi A.
      • et al.
      Metal-on-metal bearings and hypersensitivity in patients with artificial hip joints. A clinical and histomorphological study.
      Pseudotumour refers to a peri-prosthetic soft tissue mass that typically is associated with widespread tissue necrosis and ALVAL.
      • Pandit H.
      • Glyn-Jones S.
      • McLardy-Smith P.
      • et al.
      Pseudotumours associated with metal-on-metal hip resurfacings.
      The mass itself has been described as cystic, solid, or a combination of both.
      The abnormal soft tissue reaction to MoM bearing surfaces results from the deposition of cobalt-chrome particulate debris in the surrounding tissues.
      • Mahendra G.
      • Pandit H.
      • Kliskey K.
      • Murray D.
      • Gill H.S.
      • Athanasou N.
      Necrotic and inflammatory changes in metal-on-metal resurfacing hip arthroplasties.
      This is thought to be secondary to corrosive metal contact between the cobalt-chrome femoral head and metal liner, which leads to release of metal ions.
      • Campbell P.
      • Beaulé P.E.
      • Ebramzadeh E.
      • et al.
      The John Charnley Award: a study of implant failure in metal-on-metal surface arthroplasties.
      Risk factors for increased wear and metal debris include malpositioned acetabular components with an increased abduction angle (≥50°) and anteversion leading to edge loading and failure of lubrication.
      • Campbell P.
      • Beaulé P.E.
      • Ebramzadeh E.
      • et al.
      The John Charnley Award: a study of implant failure in metal-on-metal surface arthroplasties.
      It is also increasingly apparent that metal ion release can result from abnormal corrosion between the cobalt-chrome head and trunnion.
      • Haddad F.S.
      • Thakrar R.R.
      • Hart A.J.
      • et al.
      Metal-on-metal bearings: the evidence so far.
      ,
      • Gill I.P.
      • Webb J.
      • Sloan K.
      • Beaver R.J.
      Corrosion at the neck-stem junction as a cause of metal ion release and pseudotumour formation.
      ,
      • Haddad F.S.
      Metal-on-metal: more questions than answers.
      Multiple studies have identified corrosion on retrieved femoral components without any evidence of significant wear of the MoM bearing surfaces.
      • Donell S.T.
      • Darrah C.
      • Nolan J.F.
      • et al.
      Early failure of the Ultima metal-on-metal total hip replacement in the presence of normal plain radiographs.
      ,
      • Bolland B.J.
      • Culliford D.J.
      • Langton D.J.
      • Millington J.P.
      • Arden N.K.
      • Latham J.M.
      High failure rates with a large-diameter hybrid metal-on-metal total hip replacement: clinical, radiological and retrieval analysis.
      The additional head-trunnion junction present in MoM THA (compared to MoM hip resurfacing) may exacerbate and accelerate the problems associated with MoM bearing surfaces.
      • Garbuz D.S.
      • Tanzer M.
      • Greidanus N.V.
      • Masri B.A.
      • Duncan C.P.
      The John Charnley Award: metal-on-metal hip resurfacing versus large-diameter head metal-on-metal total hip arthroplasty: a randomized clinical trial.
      ,
      • Langton D.J.
      • Jameson S.S.
      • Joyce T.J.
      • et al.
      Accelerating failure rate of the ASR total hip replacement.
      A randomised control trial comparing large-head MoM THA and hip resurfacing demonstrated higher serum metal ion levels in the THA group, with no clear effect on outcomes.
      • Garbuz D.S.
      • Tanzer M.
      • Greidanus N.V.
      • Masri B.A.
      • Duncan C.P.
      The John Charnley Award: metal-on-metal hip resurfacing versus large-diameter head metal-on-metal total hip arthroplasty: a randomized clinical trial.
      Previous in vitro studies proposed that metal particulate debris induced a dose-dependent local cytotoxic response and necrosis in the peri-prosthetic soft tissues.
      • Kwon Y.M.
      • Xia Z.
      • Glyn-Jones S.
      • Beard D.
      • Gill H.S.
      • Murray D.W.
      Dose-dependent cytotoxicity of clinically relevant cobalt nanoparticles and ions on macrophages in vitro.
      This remains controversial, as recent literature suggests no association between periprosthetic tissue metal content and histological findings.
      • Lehtovirta L.
      • Reito A.
      • Parkkinen J.
      • Peräniemi S.
      • Vepsäläinen J.
      • Eskelinen A.
      Association between periprosthetic tissue metal content, whole blood and synovial fluid metal ion levels and histopathological findings in patients with failed metal-on-metal hip replacement.
      A delayed type IV hypersensitivity reaction has also been implicated as a possible cause of tissue damage in the absence of significant wear or corrosion, with similar histological findings to perivascular lymphocyte infiltration.
      • Milosev I.
      • Trebse R.
      • Kovac S.
      • Cör A.
      • Pisot V.
      Survivorship and retrieval analysis of Sikomet metal-on-metal total hip replacements at a mean of seven years.
      However, this potential aetiology remains debatable as true hypersensitivity is rare and the majority of cases with ALVAL can be explained by excessive wear or corrosion.
      • Milosev I.
      • Trebse R.
      • Kovac S.
      • Cör A.
      • Pisot V.
      Survivorship and retrieval analysis of Sikomet metal-on-metal total hip replacements at a mean of seven years.
      ,
      • Roberts T.T.
      • Haines C.M.
      • Uhl R.L.
      Allergic or hypersensitivity reactions to orthopaedic implants.
      Release of both metal ions and nanoparticles occur following abnormal wear of MoM articulations. Metal particulate debris has increased bioactivity, quantity of particles, and surface area compared to the classic larger particles from polyethylene wear.
      • Haddad F.S.
      • Thakrar R.R.
      • Hart A.J.
      • et al.
      Metal-on-metal bearings: the evidence so far.
      The metal particles are then phagocytosed by giant cells and macrophages, which leads to a release of intra-cellular metal ions and subsequent cell death.
      • Haddad F.S.
      • Thakrar R.R.
      • Hart A.J.
      • et al.
      Metal-on-metal bearings: the evidence so far.
      Macroscopically, this can manifest as soft tissue destruction, aseptic loosening, and osteolysis.
      • Haddad F.S.
      • Thakrar R.R.
      • Hart A.J.
      • et al.
      Metal-on-metal bearings: the evidence so far.
      Local metal debris is also associated with increased serum ion levels. These levels may become grossly elevated with progressive implant loosening. Studies have demonstrated systemic dissemination of metal particles in solid organs, although its clinical relevance is largely unknown. Increased exposure to cobalt and chromium has induced teratogenicity in animal models, but there is no conclusive evidence that this occurs in humans.
      • Gilani S.H.
      • Alibhai Y.
      Teratogenicity of metals to chick embryos.
      Regardless, the theoretical possibility of long-term effects, combined with lack of available literature, provides an indication for ongoing surveillance of these (often) young patients.

      3. Presentation & evaluation

      Patients with implanted MoM THAs or hip resurfacings require routine surveillance including a detailed history, physical examination, imaging, and bloodwork. Patients can be broadly divided in 2 distinct categories with different treatment algorithms: (1) asymptomatic and (2) symptomatic.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      A comprehensive history is imperative to identify current symptomatology including assessment of pain onset, severity, frequency, character & location. A detailed review of the index operation and immediate post-operative course is also important, in particular the specific implant type, surgical approach and history of wound complications. Attention should be made to rule out any evidence of local and systemic infection. While the true relationship between metal allergy and ARMD is uncertain, patients should be asked if there is a history of personal or family history of metal allergy.
      Routine physical examination includes assessment of gait and strength testing of the abductor muscles. Previous surgical incision(s) should be inspected for signs of infection and the hip should be palpated to identify any obvious soft tissues masses.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      Evaluation of range of motion and detailed neurovascular examination can help rule out other pathologies causing a painful hip. A careful history and physical exam determines the role of subsequent imaging and laboratory testing.

      4. Imaging

      Plain radiographs of the pelvis and affected hip should be reviewed to identify the implant type, size, and component position. Serial radiographs should be compared for evidence of progressive osteolysis, subsidence, and change in component position. Progressive osteolysis in the ischium, pubis, or retroacetabular regions may indicate more extensive disease with associated component loosening.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      Fracture of the femoral neck (specifically for hip resurfacing) and aseptic loosening can often be identified with plain radiography, but do not necessarily confirm underlying ARMD.
      • Haddad F.S.
      • Thakrar R.R.
      • Hart A.J.
      • et al.
      Metal-on-metal bearings: the evidence so far.
      The acetabular abduction angle should be carefully measured, as abduction angles ≥50° have been associated with increased synovial and serum metal ion levels, likely secondary to edge loading.
      • Campbell P.
      • Beaulé P.E.
      • Ebramzadeh E.
      • et al.
      The John Charnley Award: a study of implant failure in metal-on-metal surface arthroplasties.
      It is also important to recognise that the large-diameter metal femoral heads may obscure the acetabular rim, decreasing the validity of plain radiographs for assessing acetabular position.
      • Hart A.J.
      • Dandachli W.
      • Schlueter-Brust K.
      • Henckel J.
      • Cobb J.
      Large ball metal on metal hips obscure cup angle measurement on plain radiographs.
      Both ultrasound and metal artifact reduction sequences (MARS) magnetic resonance imaging (MRI) are acceptable cross-sectional imaging modalities to detect ARMD. Ultrasound is a cost-effective, quick, readily available, and non-invasive imaging test that is reliably able to detect pseudotumour. It is can also identify lesions as cystic or solid and is relatively unaffected by the presence of metal implants. It is the preferred modality for patients with contraindications to MRI, and can also be used to guide hip aspiration for histological and culture analysis.
      • Haddad F.S.
      • Thakrar R.R.
      • Hart A.J.
      • et al.
      Metal-on-metal bearings: the evidence so far.
      Ultrasound has been shown to have a sensitivity of 100% and specificity of 96%.
      • Garbuz D.S.
      • Hargreaves B.A.
      • Duncan C.P.
      • Masri B.A.
      • Wilson D.R.
      • Forster B.B.
      The John Charnley Award: diagnostic accuracy of MRI versus ultrasound for detecting pseudotumors in asymptomatic metal-on-metal THA.
      A disadvantage of ultrasound is that it is user-dependent and can be challenging to evaluate deep structures. In addition, the quality of imaging can be significantly affected in obese patients, reducing its utility.
      MARS MRI offers the ability to assess both the soft tissues and bone in the peri-prosthetic space. Advocates for MRI believe it offers an improved assessment of the extent of soft tissue damage, quality of the abductor tendons, and surrounding musculature. It is also easier to compare serial MRIs for assessing progression of disease. The sensitivity and specificity of MRI has reported to be 92% and 100%, respectively.
      • Garbuz D.S.
      • Hargreaves B.A.
      • Duncan C.P.
      • Masri B.A.
      • Wilson D.R.
      • Forster B.B.
      The John Charnley Award: diagnostic accuracy of MRI versus ultrasound for detecting pseudotumors in asymptomatic metal-on-metal THA.
      However, despite the use of metal artifact reduction sequences, prosthetic artifact can still occur and small lesions can be missed.
      • Haddad F.S.
      • Thakrar R.R.
      • Hart A.J.
      • et al.
      Metal-on-metal bearings: the evidence so far.
      MRI is also significantly more costly than ultrasound (estimated £216 vs. £49) and generally less available.
      • Lloyd J.
      • Starks I.
      • Wainwright T.
      • Middleton R.
      Metal-on-Metal resurfacing and the cost to the nation: a conservative estimate of the unexpected costs required to implement the new metal-on-metal follow-up programme in the UK.
      CT scans can be useful to accurately determine component position and assess the degree of osteolysis and residual bone stock. However, it is not as reliable as ultrasound or MRI in delineating soft tissue lesions.
      The decision to perform an ultrasound versus a MARS MRI as the initial screening tool remains controversial, with no obvious consensus. The United Kingdom Medicines and Healthcare Products Regulatory Agency (MHRA)
      • Medicines and Healthcare Products Regulatory Agency
      Medical device alert. All metal-on-metal (MoM) hip replacements: updated advice for follow-up of patients.
      recommends either ultrasound or MRI as an effective imaging modality. Garbuz et al. recommended ultrasound as an initial screening tool, citing decreased costs and the ability to reliably rule out pseudotumour in asymptomatic patients (sensitivity 100%).
      • Garbuz D.S.
      • Hargreaves B.A.
      • Duncan C.P.
      • Masri B.A.
      • Wilson D.R.
      • Forster B.B.
      The John Charnley Award: diagnostic accuracy of MRI versus ultrasound for detecting pseudotumors in asymptomatic metal-on-metal THA.
      Other authors have advocated for obtaining both MRI and US when revision surgery is planned, suggesting that combined imaging is the most effective method to identifying the presence of pseudotumour.
      • Matharu G.S.
      • Mansour R.
      • Dada O.
      • Ostlere S.
      • Pandit H.G.
      • Murray D.W.
      Which imaging modality is most effective for identifying pseudotumours in metal-on-metal hip resurfacings requiring revision: ultrasound or MARS-MRI or both?.
      The decision to perform an ultrasound or MRI as the initial screening imaging modality continues to be at the discretion of the surgeon and availability within each hospital system.

      5. Laboratory evaluation

      Routine laboratory workup for MoM arthroplasty surveillance includes a full blood count (FBC), serum C-reactive protein (CRP) level, erythrocyte sedimentation rate (ESR), and serum metal ion levels. Hip aspirate analysis can also be performed in situations where there is concern for a prosthetic joint infection.
      While elevated serum ESR and CRP levels should raise concern for infection, caution should be exercised when interpreting levels. Elevated ESR and CRP levels have both been reported in cases of non-infected pseudotumour.
      • Langton D.J.
      • Sidaginamale R.P.
      • Joyce T.J.
      • et al.
      The clinical implications of elevated blood metal ion concentrations in asymptomatic patients with MoM hip resurfacings: a cohort study.
      Serum metal ions, typically cobalt and chromium, should be routinely obtained in patients who are symptomatic, have radiographic changes, malpositioned components, or recalled implants.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      Increased cobalt levels (compared to pre-operative levels) have been demonstrated in well-functioning MoM implants, with a peak between 6- and 12-months post-operatively.
      • Brodner W.
      • Bitzan P.
      • Meisinger V.
      • Kaider A.
      • Gottsauner-Wolf F.
      • Kotz R.
      Serum cobalt levels after metal-on-metal total hip arthroplasty.
      Asymptomatic patients with well-functioning MoM hips can be expected to have serum cobalt and chromium levels of 2 parts per billion (ppb).
      Although it is accepted that grossly elevated metal ion levels raise concern for ARMD, controversy exists in determining the optimal cut-off levels. Hart et al. initially defined a cobalt and chromium cut-off level of > 7 ppb
      • Hart A.J.
      • Skinner J.A.
      • Winship P.
      • et al.
      Circulating levels of cobalt and chromium from metal-on-metal hip replacement are associated with CD8+ T-cell lymphopenia.
      which was subsequently adopted by the MHRA, Health Canada, and the Hip Society algorithm for MoM arthroplasty surveillance.
      • Medicines and Healthcare Products Regulatory Agency
      Medical Device Alert: all metal-on-metal (MoM) hip replacements.
      ,
      • Lombardi A.V.
      • Barrack R.L.
      • Berend K.R.
      • et al.
      The Hip Society: algorithmic approach to diagnosis and management of metal-on-metal arthroplasty.
      ,
      Health Canada
      Metal-on-Metal hip implants - information for orthopaedic surgeons regarding patient management following surgery - for Health professionals.
      However, there is concern that a cut-off of 7 ppb results in a high specificity but low sensitivity. In a separate study, Hart et al. determined a specificity of 89% and a sensitivity of 52% when the cut-off level was set at 7 ppb.
      • Hart A.J.
      • Sabah S.A.
      • Bandi A.S.
      • et al.
      Sensitivity and specificity of blood cobalt and chromium metal ions for predicting failure of metal-on-metal hip replacement.
      The authors subsequently recommended to lower the cut-off levels of cobalt and chromium to 4.97 ppb, with a resulting sensitivity of 63% and specificity of 86%.
      • Hart A.J.
      • Sabah S.A.
      • Bandi A.S.
      • et al.
      Sensitivity and specificity of blood cobalt and chromium metal ions for predicting failure of metal-on-metal hip replacement.
      There is also increasing evidence that an increased cobalt to chromium (Co/Cr) ratio can predict ARMD in patients with MOM THA, and in particular indicate taper corrosion.
      • Hothi H.S.
      • Berber R.
      • Whittaker R.K.
      • Blunn G.W.
      • Skinner J.A.
      • Hart A.J.
      The relationship between cobalt/chromium ratios and the high prevalence of head-stem junction corrosion in metal-on-metal total hip arthroplasty.
      ,
      • Laaksonen I.
      • Galea V.P.
      • Donahue G.S.
      • Matuszak S.J.
      • Muratoglu O.
      • Malchau H.
      The cobalt/chromium ratio provides similar diagnostic value to a low cobalt threshold in predicting adverse local tissue reactions in patients with metal-on-metal hip arthroplasty.
      However, the overall utility of metal ion levels is controversial in itself, with one systematic review and meta-analysis concluding they are not useful tests for determining ARMD in asymptomatic patients.
      • Pahuta M.
      • Smolders J.
      • van Susante J.
      • Peck J.
      • Kim P.
      • Beaule P.
      Blood metal ion levels are not a useful test for adverse reactions to metal debris: a systematic review and meta-analysis.
      While increased cobalt and chromium in isolation may not reliable in detecting ARMD, it is a useful adjunct in the evaluation of a patient with a MoM arthroplasty.
      Hip aspiration for cell count, differential, culture and sensitivities is useful in situations where there is clinical concern for a prosthetic joint infection. The sterile effusion associated with metallosis has been classically described as a watery, hazy, yellowish-grey fluid medium with a similar appearance to “dishwater fluid”.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      Fibrinous debris from MoM reactions can falsely elevate automated cell count levels, and a manual cell differential count should be performed to minimise false positives.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      Regardless, an increased cell count and elevated synovial neutrophil percentage (PMN%) should raise suspicion for infection.

      6. Treatment algorithms

      6.1 Asymptomatic patients

      The treatment strategies for patients with MoM implants are different for asymptomatic and symptomatic patients (see Fig. 1).
      • Medicines and Healthcare Products Regulatory Agency
      Medical device alert. All metal-on-metal (MoM) hip replacements: updated advice for follow-up of patients.
      Optimal follow-up and treatment for asymptomatic patients remains controversial. Measurement of serum ion levels should be measured routinely for asymptomatic patients with known risk factors for developing ARMD. These include malpositioned components (specifically an acetabular abduction angle ≥ 50°), radiographic changes suggestive of osteolysis or loosening, and patients with recalled implants. In the absence of these risk factors, annual follow-up with an Oxford Hip score assessment and plain radiographs is appropriate for asymptomatic patients.
      • Medicines and Healthcare Products Regulatory Agency
      Medical device alert. All metal-on-metal (MoM) hip replacements: updated advice for follow-up of patients.
      ,
      • Lombardi A.V.
      • Barrack R.L.
      • Berend K.R.
      • et al.
      The Hip Society: algorithmic approach to diagnosis and management of metal-on-metal arthroplasty.
      Fig. 1
      Fig. 1Management recommendations for patients with metal-on-metal hip replacement implants.
      Medicines and Healthcare Products Regulatory Agency. Management recommendations for patients with metal-on-metal hip replacement implants https://assets.publishing.service.gov.uk/media/5954ca1ded915d0baa00009b/MDA-2017-018_Final.pdf.
      • Medicines and Healthcare Products Regulatory Agency
      Medical device alert. All metal-on-metal (MoM) hip replacements: updated advice for follow-up of patients.
      Asymptomatic patients with known risk factors require measurement of serum cobalt and chromium levels. The UK MHRA,
      • Medicines and Healthcare Products Regulatory Agency
      Medical Device Alert: all metal-on-metal (MoM) hip replacements.
      Health Canada
      • Canada H.
      Metal-on-Metal hip implants - information for orthopaedic surgeons regarding patient management following surgery - for Health professionals.
      and the Hip Society
      • Lombardi A.V.
      • Barrack R.L.
      • Berend K.R.
      • et al.
      The Hip Society: algorithmic approach to diagnosis and management of metal-on-metal arthroplasty.
      (Fig. 1) all recommend 7 ppb as a cut-off for serum cobalt and chromium levels, with other authors advocating for this to be dropped to 4.97 ppb.
      • Hart A.J.
      • Sabah S.A.
      • Bandi A.S.
      • et al.
      Sensitivity and specificity of blood cobalt and chromium metal ions for predicting failure of metal-on-metal hip replacement.
      The European multidisciplinary consensus statement suggested a wide cut-off range of 2–7 ppb, acknowledging the controversies in defining a cut-off level.
      • Hannemann F.
      • Hartmann A.
      • Schmitt J.
      • et al.
      European multidisciplinary consensus statement on the use and monitoring of metal-on-metal bearings for total hip replacement and hip resurfacing.
      Patients with low serum metal ion levels can be followed up with repeat plain radiographs and metal ion levels on an annual basis.
      • Haddad F.S.
      • Thakrar R.R.
      • Hart A.J.
      • et al.
      Metal-on-metal bearings: the evidence so far.
      Asymptomatic patients with elevated cobalt and/or chromium levels should be investigated with advanced imaging. With no clear consensus on the best initial imaging test, the majority of treatment algorithms recommend either ultrasound or MARS MRI as appropriate investigations to assess for adverse soft tissue lesions.
      • Lombardi A.V.
      • Barrack R.L.
      • Berend K.R.
      • et al.
      The Hip Society: algorithmic approach to diagnosis and management of metal-on-metal arthroplasty.
      Patients with elevated serum metal ions and no evidence of fluid or mass on advanced imaging should be followed up closely every 3–6 months.
      • Lombardi A.V.
      • Barrack R.L.
      • Berend K.R.
      • et al.
      The Hip Society: algorithmic approach to diagnosis and management of metal-on-metal arthroplasty.
      Asymptomatic patients with evidence of ARMD on ultrasound or MRI remain a clinical challenge. It has been reported that soft tissue lesions will progress and become symptomatic in these patients.
      • Malviya A.
      • Holland J.P.
      Pseudotumours associated with metal-on-metal hip resurfacing: 10-year Newcastle experience.
      ,
      • Langton D.J.
      • Jameson S.S.
      • Joyce T.J.
      • Hallab N.J.
      • Natu S.
      • Nargol A.V.
      Early failure of metal-on-metal bearings in hip resurfacing and large-diameter total hip replacement: a consequence of excess wear.
      There is evidence that early intervention prior to significant soft tissue destruction leads to improved post-operative outcomes following revision THA.
      • Malviya A.
      • Holland J.P.
      Pseudotumours associated with metal-on-metal hip resurfacing: 10-year Newcastle experience.
      A detailed discussion with the patients is required, and revision surgery should be considered with increasing metal ion levels, interval radiographic changes, or onset of symptoms.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      Patients who do not subsequently undergo revision THA should be followed up closely every 3–6 months.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      ,
      • Lombardi A.V.
      • Barrack R.L.
      • Berend K.R.
      • et al.
      The Hip Society: algorithmic approach to diagnosis and management of metal-on-metal arthroplasty.

      6.2 Symptomatic patients

      Symptomatic patients require a comprehensive history and physical examination, serum metal ion levels, and advanced imaging with ultrasound and/or MARS MRI. Specific attention should be made to rule out other common causes of hip pain following arthroplasty. Patients with low metal ion levels and no evidence of fluid or mass on imaging can be closely monitored every 3–6 months with repeat ions levels and plain radiographs.
      Patients with increased serum metal ion levels but no evidence of fluid or mass on imaging represent a moderate to high risk group.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      ,
      • Lombardi A.V.
      • Barrack R.L.
      • Berend K.R.
      • et al.
      The Hip Society: algorithmic approach to diagnosis and management of metal-on-metal arthroplasty.
      Patients with low serum metal ion levels but evidence of fluid or mass on imaging also fall into this risk category.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      Revision surgery should be considered in these patients with progressive symptoms, acetabular component abduction angle ≥50°, radiographic evidence of loosening or osteolysis, and poor implant track record.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      ,
      • Lombardi A.V.
      • Barrack R.L.
      • Berend K.R.
      • et al.
      The Hip Society: algorithmic approach to diagnosis and management of metal-on-metal arthroplasty.
      The highest risk group is represented by symptomatic patients with elevated serum cobalt and chromium in combination with presence of fluid or a mass on advanced imaging. These patients are best managed with prompt revision surgery.

      7. Revision total hip replacement

      Revision surgery for MoM arthroplasty requires a clear indication and careful review of the history, physical examination, imaging, and laboratory results. Common indications for revision THA following MoM arthroplasty include progressive symptoms, malpositioned components, pseudotumour, osteolysis, loosening, instability, and periprosthetic fracture. Initial outcomes following revision THA for ARMD were poor, with reported major complication rates of 38% including instability, deep infection, recurrence of ARMD, neurovascular injury, component loosening, and reoperation.
      • Munro J.T.
      • Masri B.A.
      • Duncan C.P.
      • Garbuz D.S.
      High complication rate after revision of large-head metal-on-metal total hip arthroplasty.
      These early poor results led to the development of treatment algorithms and adoption of a lower threshold for revision surgery.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      ,
      • Lombardi A.V.
      • Barrack R.L.
      • Berend K.R.
      • et al.
      The Hip Society: algorithmic approach to diagnosis and management of metal-on-metal arthroplasty.
      Revision THA for MoM arthroplasty varies widely in complexity given the heterogenous nature of ARMD.
      • Matharu G.S.
      • Eskelinen A.
      • Judge A.
      • Pandit H.G.
      • Murray D.W.
      Revision surgery of metal-on-metal hip arthroplasties for adverse reactions to metal debris.
      Surgical goals include excision of all metallosis within the soft tissues and implantation of well-positioned components to optimise stability. Formal intra-operative photos should be taken, and specimens should be sent for culture and histology.
      • Bolognesi M.P.
      • Ledford C.K.
      Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
      Removed MoM implants should be sent for retrieval analysis.
      In the setting of minimal soft tissue damage, well-positioned components can be retained if stable. Large pseudotumours with significant soft tissue necrosis and osteolysis typically require extensive debridement and reconstruction with revision components and possible augments. Pseudotumours that involve local neurovascular structures may require assistance from a vascular or plastics surgeon for safe exposure and debridement. It is important to recognise that MoM hip resurfacing and large-head MoM THA are different entities, with taper corrosion often the aetiology of ARMD in MoM THA. If the femoral component is retained, a taper adapter should be added to the trunnion to prevent further corrosion.
      • Matharu G.S.
      • Eskelinen A.
      • Judge A.
      • Pandit H.G.
      • Murray D.W.
      Revision surgery of metal-on-metal hip arthroplasties for adverse reactions to metal debris.
      However, if significant macroscopic damage to the trunnion exists, femoral revision is necessary to prevent ongoing metal ion deposition. Patients should be revised to non-MoM bearing surfaces, with poor outcomes demonstrated when MoM bearing surfaces are used during revision.
      • Matharu G.S.
      • Pynsent P.B.
      • Sumathi V.P.
      • et al.
      Predictors of time to revision and clinical outcomes following revision of metal-on-metal hip replacements for adverse reaction to metal debris.
      It has been proposed that revision with ceramic-on-polyethylene bearing surfaces may minimise further metal wear; however, similar outcomes have been shown with metal-on-polyethylene bearing surfaces.
      • Matharu G.S.
      • Judge A.
      • Pandit H.G.
      • Murray D.W.
      Which factors influence the rate of failure following metal-on-metal hip arthroplasty revision surgery performed for adverse reactions to metal debris? an analysis from the National Joint Registry for England and Wales.
      Current literature suggests that both are appropriate to use during revision.
      • Matharu G.S.
      • Judge A.
      • Pandit H.G.
      • Murray D.W.
      Which factors influence the rate of failure following metal-on-metal hip arthroplasty revision surgery performed for adverse reactions to metal debris? an analysis from the National Joint Registry for England and Wales.
      In contrast, utilisation of ceramic-on-ceramic bearing surfaces during revision is associated with an 86% increased risk of re-revision.
      • Matharu G.S.
      • Eskelinen A.
      • Judge A.
      • Pandit H.G.
      • Murray D.W.
      Revision surgery of metal-on-metal hip arthroplasties for adverse reactions to metal debris.
      Extensive soft tissue damage to the hip capsule and abductor muscles should be anticipated. This can significantly affect inherent stability, and early studies have reported dislocation in 28% of patients undergoing for revision for ARMD.
      • Munro J.T.
      • Masri B.A.
      • Duncan C.P.
      • Garbuz D.S.
      High complication rate after revision of large-head metal-on-metal total hip arthroplasty.
      Jennings et al. also reported a dislocation rate of 22% following revision THA with an isolated head and liner exchange only.
      • Jennings J.M.
      • White S.
      • Martin J.R.
      • Yang C.C.
      • Miner T.M.
      • Dennis D.A.
      Revisions of modular metal-on-metal THA have a high risk of early complications.
      This may be related to ongoing metal ion release from corrosion of the damaged taper.
      • Hothi H.S.
      • Berber R.
      • Whittaker R.K.
      • Blunn G.W.
      • Skinner J.A.
      • Hart A.J.
      The relationship between cobalt/chromium ratios and the high prevalence of head-stem junction corrosion in metal-on-metal total hip arthroplasty.
      While isolated head and liner exchange may be appropriate in some patients, surgeons should be aware of the high risk of instability and critically evaluate component position and evidence of corrosion. A dual-mobility acetabular system or constrained liner may be necessary to obtain stability, and surgeons should have a low threshold to revise damaged or malpositioned components.
      • Matharu G.S.
      • Eskelinen A.
      • Judge A.
      • Pandit H.G.
      • Murray D.W.
      Revision surgery of metal-on-metal hip arthroplasties for adverse reactions to metal debris.
      An increased risk of post-operative infection has also been associated with revision THA for ARMD. The host response to bacteria may be influenced by metal ion-induced cytotoxicity and generation of a cell-mediated immune response.
      • Grammatopoulos G.
      • Munemoto M.
      • Inagaki Y.
      • Tanaka Y.
      • Athanasou N.A.
      The diagnosis of infection in metal-on-metal hip arthroplasties.
      Progressive soft tissue necrosis and the presence of a large effusion and pseudotumour may represent an ideal environment for infection, particularly from acute haematogenous spread.
      • Grammatopoulos G.
      • Munemoto M.
      • Inagaki Y.
      • Tanaka Y.
      • Athanasou N.A.
      The diagnosis of infection in metal-on-metal hip arthroplasties.
      In a retrospective single-institution review, Wyles et al. reported an 8.1% risk of re-operation for infection following revision THAs for MoM arthroplasty. Other described risk factors for infection include incomplete excision of necrotic tissue or metal debris, multiple operations, and retention of primary MoM components.
      • Munro J.T.
      • Masri B.A.
      • Duncan C.P.
      • Garbuz D.S.
      High complication rate after revision of large-head metal-on-metal total hip arthroplasty.
      ,
      • Liddle A.D.
      • Satchithananda K.
      • Henckel J.
      • et al.
      Revision of metal-on-metal hip arthroplasty in a tertiary center: a prospective study of 39 hips with between 1 and 4 years of follow-up.
      Outcomes following revision THA for ARMD are historically poor compared to MoM arthroplasty revised for non-ARMD indications and conventional primary THA.
      • Munro J.T.
      • Masri B.A.
      • Duncan C.P.
      • Garbuz D.S.
      High complication rate after revision of large-head metal-on-metal total hip arthroplasty.
      ,
      • Grammatopoulos G.
      • Grammatopolous G.
      • Pandit H.
      • et al.
      Hip resurfacings revised for inflammatory pseudotumour have a poor outcome.
      However, early studies generally described revision THA in the setting of extensive soft tissue necrosis and pseudotumour, which are associated with worse outcomes.
      • Haddad F.S.
      • Thakrar R.R.
      • Hart A.J.
      • et al.
      Metal-on-metal bearings: the evidence so far.
      This has led to the adoption of structured surveillance programmes and a push towards early revision prior to extensive soft tissue damage.
      • Malviya A.
      • Holland J.P.
      Pseudotumours associated with metal-on-metal hip resurfacing: 10-year Newcastle experience.
      ,
      • Haddad F.S.
      • Thakrar R.R.
      • Hart A.J.
      • et al.
      Metal-on-metal bearings: the evidence so far.
      ,
      • Grammatopoulos G.
      • Grammatopolous G.
      • Pandit H.
      • et al.
      Hip resurfacings revised for inflammatory pseudotumour have a poor outcome.
      It is likely early surgery has resulted in a decreased re-operation rate following revision. 5-year survival rates of 90% have been reported in ARMD revisions for MoM hip arthroplasty in the national joint registry in England and Wales.
      • Matharu G.S.
      • Judge A.
      • Pandit H.G.
      • Murray D.W.
      Which factors influence the rate of failure following metal-on-metal hip arthroplasty revision surgery performed for adverse reactions to metal debris? an analysis from the National Joint Registry for England and Wales.
      In another recent retrospective review of the NJR data, MoM THAs revised for ARMD had half of the risk of re-revision compared to non-ARMD revisions, even when revision for infection was excluded.
      • Matharu G.S.
      • Judge A.
      • Murray D.W.
      • Pandit H.G.
      Outcomes after metal-on-metal hip revision surgery depend on the reason for failure: a propensity score-matched study.
      Other factors that increased risk of re-revision for MoM arthroplasties revised for ARMD were high body mass index (BMI) at the time of revision surgery, modular component only revisions, use of MoM or ceramic-on-ceramic revision bearings, and acetabular bone grafting.
      • Matharu G.S.
      • Judge A.
      • Pandit H.G.
      • Murray D.W.
      Which factors influence the rate of failure following metal-on-metal hip arthroplasty revision surgery performed for adverse reactions to metal debris? an analysis from the National Joint Registry for England and Wales.
      Most subsequent studies have reported excellent functional outcomes following revision.
      • Matharu G.S.
      • Eskelinen A.
      • Judge A.
      • Pandit H.G.
      • Murray D.W.
      Revision surgery of metal-on-metal hip arthroplasties for adverse reactions to metal debris.
      ,
      • Matharu G.S.
      • Pynsent P.B.
      • Sumathi V.P.
      • et al.
      Predictors of time to revision and clinical outcomes following revision of metal-on-metal hip replacements for adverse reaction to metal debris.
      ,
      • De Smet K.A.
      • Van Der Straeten C.
      • Van Orsouw M.
      • Doubi R.
      • Backers K.
      • Grammatopoulos G.
      Revisions of metal-on-metal hip resurfacing: lessons learned and improved outcome.
      A comparison of MoM THA revisions to first time metal-on-polyethylene THA revisions reported no difference in patient reported outcomes at 1-year post-operative.
      • Mata-Fink A.
      • Philipson D.J.
      • Keeney B.J.
      • Ramkumar D.B.
      • Moschetti W.E.
      • Tomek I.M.
      Patient-reported outcomes after revision of metal-on-metal total bearings in total hip arthroplasty.
      A Medicare database review of isolated acetabular revision for MoM and metal-on-polyethylene THA also reported no difference in complication rates at 2 years. These included dislocation, infection, and re-revision.
      • Penrose C.
      • Seyler T.
      • Wellman S.
      • Bolognesi M.
      • Lachiewicz P.
      Complications are not increased with acetabular revision of metal-on-metal total hip arthroplasty.
      There is also growing evidence that ARMD revisions performed at high-volume centres have better outcomes and lower rates of complications and re-revision.
      • Lainiala O.
      • Reito A.
      • Elo P.
      • Pajamäki J.
      • Puolakka T.
      • Eskelinen A.
      Revision of metal-on-metal hip prostheses results in marked reduction of blood cobalt and chromium ion concentrations.
      ,
      • Pritchett J.W.
      One-component revision of failed hip resurfacing from adverse reaction to metal wear debris.
      Routine follow-up with plain radiography and measurement of metal ion levels is necessary following revision surgery for ARMD. Serum cobalt and chromium ion level typically decrease dramatically in the first 3 months post-revision surgery.
      • Ball S.T.
      • Severns D.
      • Linn M.
      • Meyer R.S.
      • Swenson F.C.
      What happens to serum metal ion levels after a metal-on-metal bearing is removed?.
      This drop is not as predictable in patients with pre-revision chromium levels >20 μg/L, and levels of >5 μg/L can be measured 1 year post-operative.
      • Ball S.T.
      • Severns D.
      • Linn M.
      • Meyer R.S.
      • Swenson F.C.
      What happens to serum metal ion levels after a metal-on-metal bearing is removed?.
      Regardless, measuring the trends in the metal ion levels may help identify cases of recurrent ARMD, and persistent elevation warrants investigation with ultrasound or MRI.

      8. Conclusion

      As the understanding of ARMD has evolved, MoM THA has become obsolete and MoM hip resurfacing has significantly decreased in popularity. However, a sizable population currently exist with a MoM arthroplasty in situ, and it is imperative these patients undergo routine surveillance including history, physical examination, and evaluation of metal ion levels. Ultrasound and MARS MRI both remain acceptable options to identify evidence of ARMD, with some authors advocating ultrasound as the initial investigation given its decreased cost and higher specificity. Outcomes following revision are dependent on the indication, with poor results associated with the presence of pseudotumour and abductor deficiency. Fortunately, the introduction of structured surveillance and early revision surgery prior to extensive soft tissue destruction has improved outcomes. Operative strategies for revision THA vary from exchange of modular components to extensive debridement and reconstruction with revision components. Surgeons should have a low threshold to revise damaged or malpositioned components to prevent further metal ion deposition. In addition, MoM bearing surfaces should be revised to ceramic-on-polyethylene or metal-on-polyethylene systems. While MoM THA are no longer implanted, there still is a role for hip resurfacing with the right indications and careful follow-up.

      Contributor statement

      Chang JS was responsible for manuscript preparation and submission. Haddad FS contributed to manuscript preparation and edited the paper.

      Funding

      This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

      Declaration of competing interest

      • The authors declare no competing interests.

      Appendix A. Supplementary data

      The following is the Supplementary data to this article:

      References

        • McKee G.K.
        • Watson-Farrar J.
        Replacement of arthritic hips by the McKee-Farrar prosthesis.
        J Bone Joint Surg Br. 1966; 48: 245-259
        • Charnley J.
        Total prosthetic replacement of the hip.
        Reconstr Surg Traumatol. 1969; 11: 9-19
        • Bolognesi M.P.
        • Ledford C.K.
        Metal-on-Metal total hip arthroplasty: patient evaluation and treatment.
        J Am Acad Orthop Surg. 2015; 23: 724-731
        • Pollard T.C.
        • Baker R.P.
        • Eastaugh-Waring S.J.
        • Bannister G.C.
        Treatment of the young active patient with osteoarthritis of the hip. A five- to seven-year comparison of hybrid total hip arthroplasty and metal-on-metal resurfacing.
        J Bone Joint Surg Br. 2006; 88: 592-600
        • Fisher J.
        • Jin Z.
        • Tipper J.
        • Stone M.
        • Ingham E.
        Tribology of alternative bearings.
        Clin Orthop Relat Res. 2006; 453: 25-34
        • Ball S.T.
        • Le Duff M.J.
        • Amstutz H.C.
        Early results of conversion of a failed femoral component in hip resurfacing arthroplasty.
        J Bone Joint Surg Am. 2007; 89: 735-741
        • Bozic K.J.
        • Kurtz S.
        • Lau E.
        • et al.
        The epidemiology of bearing surface usage in total hip arthroplasty in the United States.
        J Bone Joint Surg Am. 2009; 91: 1614-1620
        • Malviya A.
        • Holland J.P.
        Pseudotumours associated with metal-on-metal hip resurfacing: 10-year Newcastle experience.
        Acta Orthop Belg. 2009; 75: 477-483
        • Kwon Y.M.
        • Ostlere S.J.
        • McLardy-Smith P.
        • Athanasou N.A.
        • Gill H.S.
        • Murray D.W.
        "Asymptomatic" pseudotumors after metal-on-metal hip resurfacing arthroplasty: prevalence and metal ion study.
        J Arthroplast. 2011; 26: 511-518
        • Kwon Y.M.
        • Thomas P.
        • Summer B.
        • et al.
        Lymphocyte proliferation responses in patients with pseudotumors following metal-on-metal hip resurfacing arthroplasty.
        J Orthop Res. 2010; 28: 444-450
        • Anderson H.
        • Toms A.P.
        • Cahir J.G.
        • Goodwin R.W.
        • Wimhurst J.
        • Nolan J.F.
        Grading the severity of soft tissue changes associated with metal-on-metal hip replacements: reliability of an MR grading system.
        Skelet Radiol. 2011; 40: 303-307
        • Pandit H.
        • Glyn-Jones S.
        • McLardy-Smith P.
        • et al.
        Pseudotumours associated with metal-on-metal hip resurfacings.
        J Bone Joint Surg Br. 2008; 90: 847-851
        • Medicines and Healthcare Products Regulatory Agency
        Medical Device Alert: all metal-on-metal (MoM) hip replacements.
        • U.S. Food and Drug Administration
        Metal on metal hip implants.
        • Haddad F.S.
        • Thakrar R.R.
        • Hart A.J.
        • et al.
        Metal-on-metal bearings: the evidence so far.
        J Bone Joint Surg Br. 2011; 93: 572-579
        • Langton D.J.
        • Jameson S.S.
        • Joyce T.J.
        • Hallab N.J.
        • Natu S.
        • Nargol A.V.
        Early failure of metal-on-metal bearings in hip resurfacing and large-diameter total hip replacement: a consequence of excess wear.
        J Bone Joint Surg Br. 2010; 92: 38-46
        • Hart A.J.
        • Satchithananda K.
        • Liddle A.D.
        • et al.
        Pseudotumors in association with well-functioning metal-on-metal hip prostheses: a case-control study using three-dimensional computed tomography and magnetic resonance imaging.
        J Bone Joint Surg Am. 2012; 94: 317-325
        • Munro J.T.
        • Masri B.A.
        • Duncan C.P.
        • Garbuz D.S.
        High complication rate after revision of large-head metal-on-metal total hip arthroplasty.
        Clin Orthop Relat Res. 2014; 472: 523-528
        • National Joint Registry for England W
        Northern Ireland, and the Isle of Man. 15th annual report.
        in: Hemel Hempstead, Hertfordshire, UK: National Joint Registry Centre; 2018. 2018
        • Korovessis P.
        • Petsinis G.
        • Repanti M.
        • Repantis T.
        Metallosis after contemporary metal-on-metal total hip arthroplasty. Five to nine-year follow-up.
        J Bone Joint Surg Am. 2006; 88: 1183-1191
        • Willert H.G.
        • Buchhorn G.H.
        • Fayyazi A.
        • et al.
        Metal-on-metal bearings and hypersensitivity in patients with artificial hip joints. A clinical and histomorphological study.
        J Bone Joint Surg Am. 2005; 87: 28-36
        • Mahendra G.
        • Pandit H.
        • Kliskey K.
        • Murray D.
        • Gill H.S.
        • Athanasou N.
        Necrotic and inflammatory changes in metal-on-metal resurfacing hip arthroplasties.
        Acta Orthop. 2009; 80: 653-659
        • Campbell P.
        • Beaulé P.E.
        • Ebramzadeh E.
        • et al.
        The John Charnley Award: a study of implant failure in metal-on-metal surface arthroplasties.
        Clin Orthop Relat Res. 2006; 453: 35-46
        • Gill I.P.
        • Webb J.
        • Sloan K.
        • Beaver R.J.
        Corrosion at the neck-stem junction as a cause of metal ion release and pseudotumour formation.
        J Bone Joint Surg Br. 2012; 94: 895-900
        • Haddad F.S.
        Metal-on-metal: more questions than answers.
        Bone Joint Lett J. 2013; 95-B: 1009-1010
        • Donell S.T.
        • Darrah C.
        • Nolan J.F.
        • et al.
        Early failure of the Ultima metal-on-metal total hip replacement in the presence of normal plain radiographs.
        J Bone Joint Surg Br. 2010; 92: 1501-1508
        • Bolland B.J.
        • Culliford D.J.
        • Langton D.J.
        • Millington J.P.
        • Arden N.K.
        • Latham J.M.
        High failure rates with a large-diameter hybrid metal-on-metal total hip replacement: clinical, radiological and retrieval analysis.
        J Bone Joint Surg Br. 2011; 93: 608-615
        • Garbuz D.S.
        • Tanzer M.
        • Greidanus N.V.
        • Masri B.A.
        • Duncan C.P.
        The John Charnley Award: metal-on-metal hip resurfacing versus large-diameter head metal-on-metal total hip arthroplasty: a randomized clinical trial.
        Clin Orthop Relat Res. 2010; 468: 318-325
        • Langton D.J.
        • Jameson S.S.
        • Joyce T.J.
        • et al.
        Accelerating failure rate of the ASR total hip replacement.
        J Bone Joint Surg Br. 2011; 93: 1011-1016
        • Kwon Y.M.
        • Xia Z.
        • Glyn-Jones S.
        • Beard D.
        • Gill H.S.
        • Murray D.W.
        Dose-dependent cytotoxicity of clinically relevant cobalt nanoparticles and ions on macrophages in vitro.
        Biomed Mater. 2009; 4025018
        • Lehtovirta L.
        • Reito A.
        • Parkkinen J.
        • Peräniemi S.
        • Vepsäläinen J.
        • Eskelinen A.
        Association between periprosthetic tissue metal content, whole blood and synovial fluid metal ion levels and histopathological findings in patients with failed metal-on-metal hip replacement.
        PLoS One. 2018; 13e0197614
        • Milosev I.
        • Trebse R.
        • Kovac S.
        • Cör A.
        • Pisot V.
        Survivorship and retrieval analysis of Sikomet metal-on-metal total hip replacements at a mean of seven years.
        J Bone Joint Surg Am. 2006; 88: 1173-1182
        • Roberts T.T.
        • Haines C.M.
        • Uhl R.L.
        Allergic or hypersensitivity reactions to orthopaedic implants.
        J Am Acad Orthop Surg. 2017; 25: 693-702
        • Gilani S.H.
        • Alibhai Y.
        Teratogenicity of metals to chick embryos.
        J Toxicol Environ Health. 1990; 30: 23-31
        • Hart A.J.
        • Dandachli W.
        • Schlueter-Brust K.
        • Henckel J.
        • Cobb J.
        Large ball metal on metal hips obscure cup angle measurement on plain radiographs.
        Hip Int. 2009; 19: 323-329
        • Garbuz D.S.
        • Hargreaves B.A.
        • Duncan C.P.
        • Masri B.A.
        • Wilson D.R.
        • Forster B.B.
        The John Charnley Award: diagnostic accuracy of MRI versus ultrasound for detecting pseudotumors in asymptomatic metal-on-metal THA.
        Clin Orthop Relat Res. 2014; 472: 417-423
        • Lloyd J.
        • Starks I.
        • Wainwright T.
        • Middleton R.
        Metal-on-Metal resurfacing and the cost to the nation: a conservative estimate of the unexpected costs required to implement the new metal-on-metal follow-up programme in the UK.
        in: Total Hip Arthroplasty. 2013: 45-52
        • Medicines and Healthcare Products Regulatory Agency
        Medical device alert. All metal-on-metal (MoM) hip replacements: updated advice for follow-up of patients.
        • Matharu G.S.
        • Mansour R.
        • Dada O.
        • Ostlere S.
        • Pandit H.G.
        • Murray D.W.
        Which imaging modality is most effective for identifying pseudotumours in metal-on-metal hip resurfacings requiring revision: ultrasound or MARS-MRI or both?.
        Bone Joint Lett J. 2016; 98-B: 40-48
        • Langton D.J.
        • Sidaginamale R.P.
        • Joyce T.J.
        • et al.
        The clinical implications of elevated blood metal ion concentrations in asymptomatic patients with MoM hip resurfacings: a cohort study.
        BMJ Open. 2013; 3
        • Brodner W.
        • Bitzan P.
        • Meisinger V.
        • Kaider A.
        • Gottsauner-Wolf F.
        • Kotz R.
        Serum cobalt levels after metal-on-metal total hip arthroplasty.
        J Bone Joint Surg Am. 2003; 85: 2168-2173
        • Hart A.J.
        • Skinner J.A.
        • Winship P.
        • et al.
        Circulating levels of cobalt and chromium from metal-on-metal hip replacement are associated with CD8+ T-cell lymphopenia.
        J Bone Joint Surg Br. 2009; 91: 835-842
        • Lombardi A.V.
        • Barrack R.L.
        • Berend K.R.
        • et al.
        The Hip Society: algorithmic approach to diagnosis and management of metal-on-metal arthroplasty.
        J Bone Joint Surg Br. 2012; 94: 14-18
        • Health Canada
        Metal-on-Metal hip implants - information for orthopaedic surgeons regarding patient management following surgery - for Health professionals.
        • Hart A.J.
        • Sabah S.A.
        • Bandi A.S.
        • et al.
        Sensitivity and specificity of blood cobalt and chromium metal ions for predicting failure of metal-on-metal hip replacement.
        J Bone Joint Surg Br. 2011; 93: 1308-1313
        • Hothi H.S.
        • Berber R.
        • Whittaker R.K.
        • Blunn G.W.
        • Skinner J.A.
        • Hart A.J.
        The relationship between cobalt/chromium ratios and the high prevalence of head-stem junction corrosion in metal-on-metal total hip arthroplasty.
        J Arthroplast. 2016; 31: 1123-1127
        • Laaksonen I.
        • Galea V.P.
        • Donahue G.S.
        • Matuszak S.J.
        • Muratoglu O.
        • Malchau H.
        The cobalt/chromium ratio provides similar diagnostic value to a low cobalt threshold in predicting adverse local tissue reactions in patients with metal-on-metal hip arthroplasty.
        J Arthroplast. 2018; 33: 3020-3024
        • Pahuta M.
        • Smolders J.
        • van Susante J.
        • Peck J.
        • Kim P.
        • Beaule P.
        Blood metal ion levels are not a useful test for adverse reactions to metal debris: a systematic review and meta-analysis.
        Bone Joint Res. 2016; 5: 379-386
        • Canada H.
        Metal-on-Metal hip implants - information for orthopaedic surgeons regarding patient management following surgery - for Health professionals.
        • Hannemann F.
        • Hartmann A.
        • Schmitt J.
        • et al.
        European multidisciplinary consensus statement on the use and monitoring of metal-on-metal bearings for total hip replacement and hip resurfacing.
        Orthop Traumatol Surg Res. 2013; 99: 263-271
        • Matharu G.S.
        • Eskelinen A.
        • Judge A.
        • Pandit H.G.
        • Murray D.W.
        Revision surgery of metal-on-metal hip arthroplasties for adverse reactions to metal debris.
        Acta Orthop. 2018; 89: 278-288
        • Matharu G.S.
        • Pynsent P.B.
        • Sumathi V.P.
        • et al.
        Predictors of time to revision and clinical outcomes following revision of metal-on-metal hip replacements for adverse reaction to metal debris.
        Bone Joint Lett J. 2014; 96-B: 1600-1609
        • Matharu G.S.
        • Judge A.
        • Pandit H.G.
        • Murray D.W.
        Which factors influence the rate of failure following metal-on-metal hip arthroplasty revision surgery performed for adverse reactions to metal debris? an analysis from the National Joint Registry for England and Wales.
        Bone Joint Lett J. 2017; 99-B: 1020-1027
        • Jennings J.M.
        • White S.
        • Martin J.R.
        • Yang C.C.
        • Miner T.M.
        • Dennis D.A.
        Revisions of modular metal-on-metal THA have a high risk of early complications.
        Clin Orthop Relat Res. 2019; 477: 344-350
        • Grammatopoulos G.
        • Munemoto M.
        • Inagaki Y.
        • Tanaka Y.
        • Athanasou N.A.
        The diagnosis of infection in metal-on-metal hip arthroplasties.
        J Arthroplast. 2016; 31: 2569-2573
        • Liddle A.D.
        • Satchithananda K.
        • Henckel J.
        • et al.
        Revision of metal-on-metal hip arthroplasty in a tertiary center: a prospective study of 39 hips with between 1 and 4 years of follow-up.
        Acta Orthop. 2013; 84: 237-245
        • Grammatopoulos G.
        • Grammatopolous G.
        • Pandit H.
        • et al.
        Hip resurfacings revised for inflammatory pseudotumour have a poor outcome.
        J Bone Joint Surg Br. 2009; 91: 1019-1024
        • Matharu G.S.
        • Judge A.
        • Murray D.W.
        • Pandit H.G.
        Outcomes after metal-on-metal hip revision surgery depend on the reason for failure: a propensity score-matched study.
        Clin Orthop Relat Res. 2018; 476: 245-258
        • De Smet K.A.
        • Van Der Straeten C.
        • Van Orsouw M.
        • Doubi R.
        • Backers K.
        • Grammatopoulos G.
        Revisions of metal-on-metal hip resurfacing: lessons learned and improved outcome.
        Orthop Clin N Am. 2011; 42 (ix): 259-269
        • Mata-Fink A.
        • Philipson D.J.
        • Keeney B.J.
        • Ramkumar D.B.
        • Moschetti W.E.
        • Tomek I.M.
        Patient-reported outcomes after revision of metal-on-metal total bearings in total hip arthroplasty.
        J Arthroplast. 2017; 32: 1241-1244
        • Penrose C.
        • Seyler T.
        • Wellman S.
        • Bolognesi M.
        • Lachiewicz P.
        Complications are not increased with acetabular revision of metal-on-metal total hip arthroplasty.
        Clin Orthop Relat Res. 2016; 474: 2134-2142
        • Lainiala O.
        • Reito A.
        • Elo P.
        • Pajamäki J.
        • Puolakka T.
        • Eskelinen A.
        Revision of metal-on-metal hip prostheses results in marked reduction of blood cobalt and chromium ion concentrations.
        Clin Orthop Relat Res. 2015; 473: 2305-2313
        • Pritchett J.W.
        One-component revision of failed hip resurfacing from adverse reaction to metal wear debris.
        J Arthroplast. 2014; 29: 219-224
        • Ball S.T.
        • Severns D.
        • Linn M.
        • Meyer R.S.
        • Swenson F.C.
        What happens to serum metal ion levels after a metal-on-metal bearing is removed?.
        J Arthroplast. 2013; 28: 53-55